1. Technical Field
The field relates to sintered metal filters and methods of making and using the same to filter fluids, including in applications requiring high efficiency filtration and/or a low pressure drop across the filter.
2. Description of Related Art
Porous metal filters, for example, made from metal powder or metal fiber, are widely used in a variety of applications. For instance, in semiconductor manufacturing and other industrial processes, a very clean environment often is required to produce sensitive products. For example, in the electronics industry, inline filters are often used to filter particulate matter from fluids in order to reduce the introduction of such particulate matter into the manufacturing process for semiconductors, thereby reducing the contamination of electronic products. Fluids can comprise gases and/or liquids.
Some applications in the electronics industry use inline filters that can achieve a high efficiency rate of removal of 99.9999999%, determined at a most penetrating particle size, i.e., 9 log reduction value (9 LRV), at a rated flow. The test methodology for evaluating 9 LRV rating is described in Rubow, K. L., and Davis, C. B., “Particle Penetration Characteristics of Porous Metal Filter Media For High Purity Gas Filtration,” Proceedings of the 37rd Annual Technical Meeting of the Institute of Environmental Sciences, pp. 834-840 (1991); Rubow, K. L., D. S. Prause and M. R. Eisenmann, “A Low Pressure Drop Sintered Metal Filter for Ultra-High Purity Gas Systems”, Proc. of the 43rd Annual Technical Meeting of the Institute of Environmental Sciences, (1997); and Semiconductor Equipment and Materials International (SEMI) test method SEMI F38-0699“Test Method for Efficiency Qualification of Point-of-Use Gas Filters,” all of which are incorporated herein by reference.
Another characteristic that can be important to the electronics industry is the pressure drop across inline filters. While pressure drop can vary with the flow rate of fluid through the filter and the pressure levels of the fluid, lower pressure drops are generally preferred in the industry. This is because some process fluids, such as gases produced from vaporization of liquid sources, have limited abilities to pressurize the gas system; thus, filters with higher pressure drops could adversely reduce (restrict) the flow of process fluids. Furthermore, in a typical high purity fluid supply system each component contributes to the overall pressure drop across the system. The fluid filter is typically the most significant contributor to the total system pressure drop. Reducing pressure drop across each, or any, component reduces the overall pressure drop across the system. This is desirable to the system operator, as it allows for beneficial operation economics by reducing the system pressure supply requirements. For example, in a system that has fluid supplied by a compressed gas cylinder, more of the volume of the gas can be accessed for wafer processing by reducing pressure drop across the system.